JPH0714828B2 - Method for reforming smelting reduction slag - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for reforming smelting reduction slag, and in particular, it effectively prevents dusting and expansion phenomena during cooling of steelmaking slag, thereby improving earth-building materials and the like. It is intended to make effective use of

(Prior Art) It is known that stainless steel slag is all powdered when the basicity (CaO / SiO ₂ ) is 1.5 or more (eg Seki Akira et al., Kawatetsu Technical Report (1986) vol. 18, No. 1.P20-24). A Such powdering is transferred to α'-2CaO · SiO ₂ is γ-2CaO · SiO _2,
It is thought to be caused by the volume expansion (about 14%) at that time. Regarding such a phase transition of 2CaO.SiO ₂ , α-type, α'-type, β-type and γ-type are known in order from high temperature, and the transition sequence and transition temperature are as follows.

Normally, it changes from α type → α'type → γ type,
Under certain conditions, it is known to transfer from α'type to β type, and since volume expansion hardly occurs at the time of this α'type to β type transition, α It is only necessary to transfer from the'type to the β type.

The α′-type to β-type transition has been studied for a long time in the field of inorganic chemistry, and various methods shown in Table 1 below have been proposed.

Of the above methods, since there is a small ion That B ^3+, effective and certainty how to Si ⁴⁺ substituted with such P ⁵⁺ ion radius than Si ⁴⁺ of (1), B ³⁺ and P ^{55 and the} like are called β-type stabilizers.

Regarding slag stabilization, borate can be stabilized not more than 1/4 compared to phosphate (Seki Akira et al., Kawatetsu Technical Report 18 (1986) 1.20-24).
Since it is also inexpensive, borate is advantageous as a slag dusting inhibitor.

Table 2 shows the composition of the stainless steel slag and the ordinary steel slag.

As is clear from the table, there are differences in both components,
2CaO / SiO ₂ exists, but ordinary steel slag does not powder.
The reason is considered to be that P ₂ O ₅ plays a role of β-type stabilizer in ordinary steel slag.

Other Another way to prevent the powdered slag, rather than 2CaO · SiO _2, it is conceivable in the form of CaO · SiO _2, For this purpose, it is necessary to add SiO ₂ about 20%. However, adding about 20% of SiO ₂ to the molten slag,
In addition, it is extremely difficult to dissolve uniformly, and it is practically impossible.

Now, as a method of modifying a stainless steel slag using a borate, there are JP-A-55-128518 and JP-A-61-
There is a method disclosed in Japanese Patent No. 111947. In the former, 0.4 to 5 wt% of B ₂ O ₃ is added to the molten slag during melting of stainless steel (hereinafter simply referred to as%
Is added) and cooled to 300 ° C. at a cooling rate of 22 ° C./min or more to prevent pulverization. On the other hand, the latter is a method for reforming a steelmaking slag, which comprises adding to the stainless steel molten slag boron oxide whose crystal water is adjusted to 4 to 12% in order to prevent powdering during cooling of the slag.

(0005) among the prior art described above, the method disclosed in JP-A-55-128518 is, B ₂ O ₃ which requires 0.4 to 5% ones large amount of B ₂ O ₃ additive This is a technology with a low yield, and because boron ore is almost unobtainable like Japan, it cannot help but be relied upon for imports from foreign countries, and it is impractical in view of its high price. Also, the method of adding boron oxide into the slag is
Because it is a method of placing it in the slag pot before,
It is considered that B ₂ O ₃ could not be uniformly dispersed, and therefore the cooling rate of the slag was set to 22 ° C./min or more, and a large amount of B ₂ O ₃ had to be added. There was also room for improvement in terms.

On the other hand, in the method disclosed in JP-A-61-111947, in order to uniformly disperse B ₂ O ₃ in the slag, it is indispensable to use a borate mineral in which the water of crystallization is adjusted to 4 to 12%. In order to control such water of crystallization, the additive is preheated to a temperature of 500 to 600 ° C and the remaining water of crystallization is 4 to
It was necessary to carry out dehydration operation so that it would be 12%, leaving a problem where labor and cost were high.

The present invention advantageously solves the above problems, and effectively reforms slag with a minimum required amount of boron oxide without wasting it, and simply and at low cost. The purpose is to propose a new method that can

(Means for Solving the Problem) That is, the present invention relates to a molten slag mainly composed of dicalcium silicate generated along with the smelting reduction of iron ore or chrome ore in an iron bath refining furnace, at the time of cooling the slag. When adding boron-containing oxides to prevent pulverization and modifying the slag, boron-containing oxides were added to the furnace at a bath temperature that did not reduce boron oxides to boron during smelting reduction refining. Is a method for reforming the smelting reduction slag.

In the present invention, when the boron-containing oxide is charged into the furnace, the bath temperature is preferably 1620 ° C. or lower, and the amount of the boron-containing oxide added is such that the B ₂ O ₃ concentration in the slag is 0.10. ~
It is advantageous that the amount is 0.40%.

Furthermore, as the boron-containing oxide used in the present invention, borax, kernite, olivine and soda ash are particularly advantageously suited.

(Operation) The present invention will be specifically described below.

To evenly disperse B ₂ O ₃ in the slag, rather than placing a boron oxide (eg, colemanite) in the ladle,
Refining furnace It is considered more effective to put it in the furnace, and as shown in FIG. 1, it is placed in the ladle pan 1 (A
Method) and a method of charging the mixture into the furnace 2 from the inversion furnace or the furnace hopper (method B) and comparing the effect of addition. The time of charging into the furnace was the final stage of smelting reduction blowing of chromium ore and about 3 to 4 minutes before tapping. The smelting reduction was carried out using a top-bottom blow K-BOP.

Other conditions are shown in Table 3 below.

The colemanite addition experiment was performed for a total of 7 charges. The modified slag is 1 to 1.5 after adding colemanite.
After the lapse of time, the slag was poured into a slag cooling yard, and the air-cooled and solidified slag was separated into a slag and a slag (slag attached to a ladle) and carried out and stored.

The experimental results obtained are summarized in Table 4.

Further, as shown in FIG. 2, the yield of B ₂ O ₃ was 50 to 75% when the modification was sufficient, and no clear difference due to the addition method was observed.

Furthermore, FIG. 3 shows the results of investigations on the uniform diffusion of B ₂ O _{3 into} the slag by each addition method. The uniformity was evaluated by the ratio of the B ₂ O ₃ concentration of each of the glass and slag.

As is clear from the figure, the concentration ratio when charged into the furnace was almost 1.0, which was uniform, while the concentration ratio varied greatly when placed in a ladle pan.

From the above experiments, it became clear that in-furnace injection is more effective for uniformly dispersing B ₂ O ₃ in the slag. Moreover, this method of charging in the furnace has an advantage that it is not necessary to control the water of crystallization of boron oxide.

Next, when adding boron oxide into the furnace, boron oxide is reduced by carbon in the slag or carbon in molten iron to become boron, and there is a concern that the molten iron will be contaminated. The conditions under which B ₂ O ₃ was reduced by C were investigated thermodynamically.

The following equation is obtained from × 2-.

2C (S) + 2 / 3B ₂ O ₃ (S) = 2CO (g) + 43B (S) ΔG ° = 141170−75.05T ... ΔG ° = 0 is at 1881K (= 1608 ° C).

Since the temperature of the slag during blowing is almost equal to the temperature of molten iron, it is considered necessary to blow at a molten iron temperature of 1608 ° C or lower.

Therefore, the relationship between the molten iron temperature and the B concentration in steel was investigated. The% B ₂ O ₃ in the slag was added with a boron oxide content of 0.15 to 0.40% so that it could be sufficiently improved. Further, B in the hot metal is 0.0001 to 0.0003%.

The results are shown in FIG.

As apparent from the figure, but is hardly reduced up to 1610 ° C., 1620 ° C. is B ₂ O ₃ is reduced in the slag Doing blowing at a temperature greater than, to dissolve in the steel, in steel B It can be seen that the concentration rises sharply. From this, it was found that it is preferable to perform the blowing temperature at 1620 ° C or lower.

If a large amount of stainless steel scrap is used,
Since B may increase due to B contained in the scrap, it is preferable to carry out at a bath temperature at which the added boron oxide is not reduced as much as possible.

Further, as is apparent from FIG. ₂ above, it is particularly advantageous that the B ₂ O ₃ concentration in the slag is 0.10% or more, as the amount of boron oxide added required for modifying the slag. I understood.

On the other hand, since boron also promotes slag slag formation, it was feared that the addition of too much of this would adversely affect the refractory material.Therefore, the relationship between the wear rate of the refractory material and the boron oxide concentration in the slag. Was also investigated.

That is, the rate of refractory wear (mm) according to% B ₂ O ₃ in the slag
/ ch), and the wear rate when B ₂ O ₃ was not added was 1.0, and the wear rate at each% B ₂ O ₃ was evaluated as an index.

The obtained results are shown in FIG.

As is clear from the figure, it was found that when% B ₂ O ₃ in the slag exceeds 0.4%, wear progresses significantly.

(Example) In a top-bottom blowing converter K-BOP, smelting reduction blowing of chromium ore was performed, and boron-containing oxide (colemanite) was added at the end of blowing.
Was added to perform slag modification.

Examples will be specifically described below. Blowing temperature is 1560 ~ 1580 ℃
I did it in. The composition of each material used in this experiment is shown in Tables 5 to 9 below.

Colemanite having the composition shown in Table 9 was discharged from the furnace bunker to the furnace hopper at the final stage of smelting reduction and 3 to 4 minutes before the end of blowing. Regarding the amount of addition, the amount of slag produced was calculated from the amount of the charge in the furnace by the following formula, and 0.35% of the amount of slag produced was added according to the formula.

The slag was sampled during tapping, and the B ₂ O ₃ yield and slag composition were investigated.

Table 10 shows some of the experimental results.

Further, on the basis of this result of these experiments, B ₂ O ₃ amount and in slag (% B ₂ O ₃₎ and was examined results shown in FIG. 6, B ₂
The O ₃ yield is about 75%.

When B ₂ O ₃ was added to the slag, it was feared that B would dissolve into the molten steel. Therefore, regarding the experimental charge with B ₂ O ₃ added in the smelting reduction furnace and the normal charge with no addition, B was mixed into the slab. investigated. Table 11 shows an example of the results.

The corner sample analysis revealed that the B concentration was about 0.0001 to 0.0004% even with the charge added with B ₂ O ₃ , indicating that B was not mixed in the slab.

Further, the modified slag was subjected to an application investigation as a road material based on the test outline shown in Table 12.

The results obtained are shown in Table 13. The grain size is 40 mm or less, which is often used for road materials.

The test results in Table 13 revealed the following.

Abrasion weight loss… By solidifying, slag on a par with rocks can be obtained. The hardness was measured by the abrasion test in the aggregate test of road materials, and 11 to 20% was obtained. This is a little harder than blast furnace slag and limestone (about 30%) and equivalent to Hanaoka rock and basalt (about 20%).

Unit volume mass: Blast furnace slag 1.6 to 1.8, ordinary steel converter slag 1.9 to 2.2, stainless slag 1.0 (powder), blast furnace,
Similar to ordinary steel converter slag.

Absolute dry specific gravity… Heavier than blast furnace slag 2.4 to 2.6, but there is no problem according to the standard Water absorption rate… It is almost the same as blast furnace slag 2.0 to 4.0.

80 ℃ water immersion expansion ... Blast furnace slag 0.01, ordinary steel converter slag 3.
From 0 to 10.0, it is worse than the blast furnace slag, but much better than the steelmaking converter slag.

Table 14 shows the results of the dissolution test conducted on slag sampled at four locations according to the Environmental Agency Notification No. 13.
However, there was no problem.

(Effects of the Invention) Thus, according to the present invention, since the boron-containing oxide can be uniformly diffused in the slag, a smaller amount of the stabilizer (boron oxide) can be used to effectively prevent pulverization. As a result, modification of the slag is achieved with a small amount of expensive stabilizer.

Further, in the past, the stabilizer also had to be pre-treated such as controlling the crystal water of the stabilizer, whereas the addition method according to the present invention does not require control of the crystal water, etc. Can be used directly.

Further, in the present invention, since B ₂ O ₃ is uniformly dispersed in the slag, the slag can be sufficiently cooled by natural cooling.

Therefore, according to the present invention, it has become possible to effectively use slag, which has conventionally been used for pulverization and has been discarded without being used, and which has been an environmental problem, as an earth building material and the like, and a great advantage can be obtained.

[Brief description of drawings]

Figure 1 a, Figure b is showing, respectively, the supply procedure of the slag modifier, FIG. 2, B ₂ O ₃ amount and graphs showing the relationship between the in% B ₂ O ₃ slag, third Figure is a graph showing the relationship between B ₂ O ₃ yield and (rough / slag) concentration ratio, Figure 4 is a graph showing the relationship between molten iron temperature and B concentration in molten iron, and Figure 5 is Fig. 6 is a graph showing the relationship between% B ₂ O ₃ in slag and the refractory wear rate index, and Fig. 6 is a graph showing the relationship between B ₂ O ₃ addition amount and% B ₂ O _{3 in} slag. .

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-64-65049 (JP, A) JP-A-62-162657 (JP, A)

Claims (3)

[Claims] 1. A molten slag composed mainly of dicalcium silicate generated by smelting reduction of iron ore or chromium ore in an iron bath refining furnace, and boron-containing oxidation for preventing slag from being pulverized during cooling. In order to modify the slag by adding substances, during melting reduction refining, the boron-containing oxide is charged into the furnace at a bath temperature at which boron oxide is not reduced to boron. Reforming method of reducing slag. 2. The method for modifying a smelting reduction slag according to claim 1, wherein the bath temperature is 1620 ° C. or lower. 3. The B ₂ O ₃ in the slag according to claim 1 or 2.
A method for reforming a smelting reducing slag, which comprises adding an amount of a boron-containing oxide to a concentration of 0.10 to 0.40 wt%.